The present invention includes a method and apparatus for encoding and playing back full-screen flicker-free plano-stereoscopic movies using a personal computer (PC) equipped with a DVD (Digital Versatile Disc) player and a cathode ray tube (CRT) monitor. The term “movies” as used herein denotes a succession of still images, whether photographed from the visual world by means of a motion picture or video camera, produced by means of a computer, or any other means, which when played back in rapid succession give the illusion of motion. The term plano-stereoscopic denotes a stereoscopic image made up of two planar perspective views (a stereo-pair). For the sake of brevity, throughout this disclosure, we will usually use the term stereoscopic. We are using the term video to denote a raster-based electronic moving image created from a succession of a fields or pictures.
We have chosen to focus our efforts on playing back recorded stereoscopic movies on a PC screen rather than on a television screen. A TV set is an appliance with a fixed vertical rate, which in the United States is 60 fields per second. This frequency is set in manufacture of the set and cannot be altered. For the display of flicker-free stereoscopic field-sequential movies, a vertical rate of at least half again more is required.
PCs often incorporate a DVD player and a CRT monitor for display. Such a PC has the necessary digital storage and processing power to decode the stereoscopically-formatted DVD we disclose here. We shall discuss how the PC components and the Stereoscopic Media (or Movie) Player (SMP) we have devised work together to help achieve our goal of playing back a flicker-free stereoscopic field-sequential movie.
In the field-sequential approach, a succession of left and right images alternate, and these left and right images form a stereoscopic moving image. The user wears a selection device (i.e., eyewear) which alternately blocks the stream of images of one perspective and passes the stream of images of the other perspective. The eyewear use a pair of liquid crystal shutters that operate out of phase with each other but in synchrony with the vertical field rate of the video signal. Products like these have been manufactured for two decades by StereoGraphics Corporation, San Rafael, Calif., the company that introduced flicker-free field-sequential stereoscopic electronic images. This art is described in the following patents: U.S. Pat. No. 5,572,250 entitled Universal Electronic Stereoscopic Display; U.S. Pat. No. 5,463,428 entitled Wireless Active Eyewear For Stereoscopic Applications; U.S. Pat. No. 5,416,510 entitled Camera Controller For Stereoscopic Video System; U.S. Pat. No. 5,239,372 entitled Stereoscopic Video Projection System; U.S. Pat. No. 5,193,000 entitled Multiplexing Technique For Stereoscopic Video System; U.S. Pat. No. 5,181,133 entitled Drive Method For Twisted Nematic Liquid Crystal Shutters For Stereoscopic And Other Applications; U.S. Pat. No. 5,117,302 entitled High Dynamic Range Electro-Optical Shutter For Stereoscopic And Other Applications; U.S. Pat. No. 4,967,268 entitled Liquid Crystal Shutter System For Stereoscopic And Other Applications; U.S. Pat. No. 4,884,876 entitled Achromatic Liquid Crystal Shutter For Stereoscopic And Other Applications; U.S. Pat. No. 4,792,850 entitled Method And System Employing A Push-Pull Liquid Crystal Modulator; U.S. Pat. No. 4,583,117 entitled Stereoscopic Video Camera; U.S. Pat. No. 4,562,463 entitled Stereoscopic Television System With Field Storage For Sequential Display Of Right And Left Images; and U.S. Pat. No. 4,523,226 entitled Stereoscopic Television System.
With reference to FIG. 1a, we see a person (107) using the principal hardware components employed for viewing stereoscopic movies with a PC. The strength of our invention is that it is able to use these commonly employed components. It is our desire to be entirely compatible with the existing infrastructure of devices commonly employed in order to gain the greatest possible audience. Our system is designed to work with any PC (101) employing a DVD player (102, shown for purposes of illustration with its caddy open). The monitor (103) is shown with an image on the CRT display screen (104), the image appearing to be doubled, as would be the case for a field-sequential stereoscopic image seen without wearing shuttering eyewear. An infrared (IR) emitter (105) is emitting IR pulses (106) which communicate with a receiver (not shown) in the selection device, active eyewear (108). Both PC and monitor are made to run at a flicker-free field rate as will be described below.
The DVD is a medium designed to play at a fixed field rate of 60 fields per second (in the United States), which is too low to be flicker-free in the stereoscopic mode, as noted above. It is a format that uses a form of compression, actually a series of techniques, known as MPEG-2. This protocol has characteristics that might destroy stereoscopic content. The MPEG-2 protocol uses a form of compression in the temporal dimension that would, for some formats such as the interlaced method, ruin stereoscopic content by blending left and right fields. Therefore, it was necessary for us to devise a means that will preserve the integrity of the perspective components of the plano-stereoscopic image. This had to be accomplished in the context of the existing infrastructure relying on standard MPEG-2 compression.
Another aspect of the invention is that we had to devise a means for taking our compressed stereoscopic images and decompressing them in a format that will play on any non-stereo ready PC, video accelerator board and other hardware components notwithstanding. It is also important to realize that this might be accomplished with the addition of a specialized hardware solution, namely a video add-on board. However, the typical user is not inclined to add boards to his or her PC, so an entirely software solution was sought for our SMP. Yet another aspect of our SMP is a means for playing back a stereoscopic image at a high enough field rate so it will be flicker-free. This must be accomplished despite the fact that the DVD medium and the PC infrastructure do not take our goal into account and are designed to work at a lower refresh rate.
We have conceived of and developed a multiplexing and de-multiplexing approach that maximizes sharpness and image quality, in a form that is compatible with the standard DVD and MPEG-2 protocols. As has been stated, we sought to achieve our end without the need for the user to add an additional video processing board to his or her PC. Thus we have achieved our end by devising a software based media player, namely our SMP.
The means for accomplishing these ends, which we have achieved in our laboratory, are described below.